I tried this:
(defn hit-or-miss
[a k v]
(if (c/has? @a k)
(c/hit @a k)
(c/miss @a k v)))
(def acu (atom (c/ttl-cache-factory {} :ttl 20000)))
(swap! acu hit-or-miss :e 55)
But I got:
ClassCastException clojure.core.cache.TTLCache cannot be cast to
clojure.lang.IDeref clojure.core/deref (core.clj:2080)
Any ideas?
On Tuesday, October 23, 2012 1:03:10 AM UTC+3, Sean Corfield wrote:
>
> Just to clarify, hit does nothing for TTL (since items timeout based
> solely on when they were added, not when they were last touched), so
> swap! on the hit really makes no difference here. It would, however,
> be required for some of the other types of cache.
>
> Also, exactly how you use has? / hit / miss is going to depend on how
> you're interacting with the cache and what behavior you want.
>
> For example, at World Singles, we use TTL caches and have three
> operations:
> * evict - this uses swap! and cache/evict to remove a cache entry
> * fetch - this uses get to return an entry if present
> * store - this uses swap! and cache/miss to add/update a cache entry
>
> Since hit doesn't do anything on a TTL cache, we don't bother calling
> it. If we switch to other types of cache, our fetch operation would
> need to be updated to use cache/has?, swap! and cache/hit (as well as
> get), or we'd need to change our API somewhat...
>
> It's my understanding that you can use assoc / dissoc on a cache as
> synonyms for miss / evict (that seemed to be true with the version of
> core.cache that I initially used - I'm fairly confident it's still
> true of assoc but not so confident that dissoc still works that way...
> maybe Fogus can help me out there?).
>
> Sean
>
> On Mon, Oct 22, 2012 at 2:31 PM, Sean Corfield
> <seanco...@gmail.com<javascript:>>
> wrote:
> > On Mon, Oct 22, 2012 at 1:50 PM, Hussein B.
> > <hubag...@gmail.com<javascript:>>
> wrote:
> >> c3 holds a map containing {:a 1} that will lives for two minutes.
> >
> > In the code I provided, c3 is an atom that holds a cache (which is the
> map).
> >
> >> After two minutes, requesting :a is generating false since it reached
> its
> >> TTL but it will still live in map until it is removed explicitly by
> invoking
> >> evict.
> >
> > Because the cache itself is immutable. That's why you need to store
> > the cache in an atom (so the atom can be updated to contain the
> > modified cache):
> >
> > (defn hit-or-miss
> > "Given an atom containing a cache, a key, and a value, update the
> > cache and return..."
> > [a k v]
> > (if (cache/has? @a k)
> > (cache/hit @a k)
> > (cache/miss @a k v)))
> >
> > ... (swap! c3 hit-or-miss :c 42) ...
> >
> >> On Monday, October 22, 2012 11:15:06 PM UTC+3, Sean Corfield wrote:
> >>> In other words you need something like this:
> >>>
> >>> (def c3 (atom (cache/ttl-cache-factory {:a 1} :ttl 20000)))
> >>> user=> @c3
> >>> {:a 1}
> >>> user=> (cache/has? @c3 :a)
> >>> true
> >>> user=> (cache/has? @c3 :a)
> >>> false
> >>> user=> @c3
> >>> {:a 1}
> >>> user=> (swap! c3 cache/evict :a)
> >>> {}
> >>> user=> @c3
> >>> {}
>
>
>
> --
> Sean A Corfield -- (904) 302-SEAN
> An Architect's View -- http://corfield.org/
> World Singles, LLC. -- http://worldsingles.com/
>
> "Perfection is the enemy of the good."
> -- Gustave Flaubert, French realist novelist (1821-1880)
>
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